The present invention relates to a process and system for treating wastewater in a constructed wetland facility.
The use of constructed wetlands for the treatment of wastewater is becoming an 3increasingly popular option especially in rural or lightly developed areas. Constructed wetlands use wetland plants and bacteria to remove pollutants from the wastewater.
Existing constructed wetlands, including surface water and subsurface flow systems, use wetland plants and atmospheric diffusion to transfer oxygen into the water. At the inlet-to the constructed wetlands, the high concentration of organic matter in the wastewater provides a rich energy source for biological activity. This activity is so vigorous that any oxygen transferred into the water is immediately consumed resulting in an essentially oxygen-free (anaerobic) zone. The organic material is consumed by the biological activity so that, as the wastewater flows through the wetland, the concentration of organic matter is rapidly reduced. The reduction in the energy source represented by the organic matter reduces the rate of microbiological activities such that an anoxic regime is formed wherein the oxygen transferred into the water is not necessarily immediately consumed but the water is still oxygen starved. The plants and water surface can provide natural aerobic zones within the constructed wetland, especially in the anoxic zone. These aerobic zones provide for efficient conversion of ammonia or ammonium ions into nitrates. The nitrates are bacteriologically reduced to nitrogen gas but such microbiological activity is inhibited by the presence of free oxygen in the aerobic zones and the anoxic zones.
A number of processes and systems have been developed to increase the aerobic activity in a constructed wetland to improve the conversion of ammonia/ammonium to nitrates. For example, U.S. Pat. No. 5,893,975 discloses a subsurface flow constructed wetland including a wastewater treatment system having a flow intake, a pretreatment nutrient addition chamber and a wastewater flow divider. The flow divider further has a compressed air aerator in the bottom thereof. An object of the invention of U.S. Pat. No. 5,893,975 is to install a supplemental air diffuser system along the bottom of the influent distribution chamber therein to facilitate initial precipitation of sludge and to prevent potential septic and/or anaerobic conditions at the initial point of treatment to significantly enhance system performance.
U.S. Pat. No. 6,126,827 discloses a wastewater treatment system wherein the liquid component is subjected to a two-part treatment wherein the first part of the treatment is carried out on a sequencing batch reactor and the second part is carried out in at least one reed bed. The wastewater entering the reed bed is comparable in quality to secondary treated wastewater except that a substantial amount of total nitrogen has also been removed.
U.S. Pat. No. 6,159,371 discloses constructed wetlands, utilizing a plurality of cells, in which nitrification and denitrification occurs simultaneously at low flow rates and lower temperatures.
The constructed wetland provides improved remediation in a shorter period of time.
U.S. Pat. No. 6,200,469 B1 discloses a system for removing pollution from water, utilizing a subsurface constructed wetland system using forced bed aeration and variable water levels, to promote greater root depth and better root structure of the wetland vegetation, and to establish staged anaerobic and aerobic zones within the system.
None of the prior art systems provide for denitrification of the wastewater in a highly anaerobic, nutrient rich zone near the inlet of the constructed wetlands. It is a hallmark of the current invention to provide for denitrification of wastewater in the anaerobic nutrient rich zone at the inlet to the constructed wetland.
The present invention provides a process and system for enhanced nitrogen removal in a wetland wastewater treatment facility that overcomes the aforementioned problems.
In a preferred embodiment, a constructed wetland wastewater treatment system is provided comprising: a constructed wetland comprising a reservoir defining a flow channel for the wastewater, the wastewater at least partially filling the reservoir, the reservoir having a lower surface, an inlet end where wastewater to be treated is introduced into the reservoir and an outlet end where treated water is discharged from the reservoir, wherein the water flows from the inlet end toward the outlet end; a source of pressurized air; a gas distributor in fluid communication with the source of pressurized air, the gas distributor being immersed in the water at least partially filling the reservoir at a location at or proximate to the lower surface and between the inlet end and the outlet end; and, a recycle system capable of moving treated water from the outlet end to the inlet end.
In another preferred embodiment, a constructed wetland wastewater treatment system is provided comprising: a constructed wetland comprising a reservoir defining a flow channel for the wastewater, the wastewater at least partially filling the reservoir, the reservoir having a lower surface, an inlet end where wastewater to be treated is introduced into the reservoir and an outlet end, wherein the water flows from the inlet end toward the outlet end; means for distributing air into the water at least partially filling the reservoir; and means for recycling treated water from the outlet end to the inlet end.
In still another preferred embodiment, a constructed wetland wastewater treatment system is provided comprising: a constructed wetland comprising a reservoir defining a flow channel for the wastewater, the wastewater at least partially filling the reservoir, the reservoir having an inlet end where wastewater to be treated is introduced into the reservoir, an outlet end where treated water is discharged from the reservoir, at least two sides, each side having an upstream end connected to the inlet end of the reservoir and a downstream end connected to the outlet end of the reservoir, and a bottom surface connected to the inlet end, the outlet end and the at least two sides, wherein the wastewater flows from the inlet end toward the outlet end; a source of pressurized air; a gas distributor in fluid communication with the source of pressurized air, the gas distributor being immersed in the wastewater at least partially filling the reservoir and extending substantially from one side of the reservoir to the other side of the reservoir at a location between the inlet end and the outlet end, such that, when air is distributed through the gas distributor, the wastewater in the reservoir is divided into an overall anaerobic zone proximate to the inlet, an overall aerobic zone proximate to the gas distributor and an overall anoxic zone proximate to the outlet end; and, mans for recycling treated water from the outlet end to the inlet end.
In yet another embodiment of the invention, a process is provided for improved nitrogen removal from wastewater treated in a constructed wetland wastewater system, the process comprising the steps of: providing a constructed wetland having an inlet end, an outlet end and means for distributing air located in the wetland intermediate to the inlet end and the outlet end and means for recycling water, the wetlands adapted to facilitate flow of wastewater from the inlet end to the outlet end; introducing wastewater to the wetland at or proximate to the inlet end, the wastewater comprising nitrogen containing organic material; allowing the wastewater to flow from the inlet end to the outlet end; allowing overall anaerobic conditions to form in the wastewater proximate to the inlet end and overall anoxic conditions to form in the wastewater proximate to the outlet end; introducing air into the wastewater through the means for distributing air such that an overall aerobic zone is formed in the wastewater proximate to the means for distributing air intermediate to the overall anaerobic zone and the overall anoxic zone, the zones situated such that the overall aerobic zone provides a substantially complete separation of the overall anaerobic zone from the overall anoxic zone; draining water from the outlet end of the wetland; and recycling some of the water drained from the outlet end to the inlet end of the wetland.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.